Dynamic random access memory device

ABSTRACT

A dynamic random access memory device which comprises one-transistor, one-capacitor-type memory cells (C 00  ˜C 127 ,127) in rows and columns and dummy cells (DC 20  &#39;˜DC 2 ,127 &#39;, DC 20  &#34;˜DC 2 ,127 &#34;, DC 20  &#34;&#39;˜DC 2 ,127 &#34;&#39;) in rows. The capacitors (C d ) of the dummy cells are charged to a high power supply potential (V CC ) by one or more charging transistors (Q A  or Q A  &#39;) clocked by a reset clock signal (φ R ). The capacitors (C d ) of the dummy cells are discharged to a low power supply potential (V SS ) by one or more transistors (Q B  or Q B  &#39;) clocked by an operation clock signal (φ WL ) having a potential lower than the high power supply potential (V CC ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, more particularly, to a dynamic random access memory (RAM) device comprising one-transistor, one-capacitor-type memory cells.

2. Description of the Prior Art

In a MOS dynamic RAM device, one-transistor, one-capacitor-type memory cells have been put to practical use, and, in addition, such memory cells are often used since they are advantageous in respect to integration density. In this type of memory cell, each cell comprises a capacitor and a transistor which serves as a switching element for charging and discharging the capacitor. Therefore, the presence or absence of charges in the capacitor represents data "1" or "0", respectively. The memory cells are arranged at intersections between word lines and bit lines. In addition, dummy cells are arranged at intersections between dummy word lines and bit lines.

In the prior art, these dummy cells are similar in construction to the one-transistor, one-capacitor-type memory cells in that they comprise a capacitor, a transistor, and an additional transistor for resetting the capacitor. However, in recent years, dummy cells comprising only one capacitor have been developed (See: IEEE Journal of Solid-State Circuits, vol. SC-15, No. 2, pp. 184-189, April 1980). A dynamic RAM including such one-capacitor dummy cells is advantageous in respect to integration density and reduces the load of the operation clock generator.

In a dynamic RAM device including the above-mentioned one-capacitor-type dummy cells, a discharging transistor and a charging transistor are provided in series between two power supplies (V_(CC), V_(SS)), and their connection node is connected to a dummy word line connected to the dummy cells. The control of this device is carried out as follows. First, the dummy word line is discharged by the discharging transistor clocked by a reset clock generator. In this state, the dummy word line is at level V_(SS). Then, the dummy word line is charged by the charging transistor clocked by an operation clock generator so that the potential of the dummy word line is pushed up to the power supply voltage (V_(CC)).

In the above-mentioned dynamic RAM device, however, in order to push up the potential of the dummy word line, the operation clock generator must generate a potential higher than V_(CC) +V_(th), where V_(th) is the threshold voltage value of the charging transistor. As a result, the operation clock generator has to incorporate a charge-pumping circuit or a bootstrap circuit for generating such a higher potential. Therefore, the operation clock generator becomes complex, and, accordingly, the operation speed of the operation clock generator, that is, the access speed of the device, becomes low.

SUMMARY OF THE INVENTION

It is, therefore, a principle object of the present invention to provide a dynamic RAM device comprising one-transistor, one-capacitor-type memory cells in which the access speed is high.

It is another object of the present invention to provide a dynamic RAM device comprising one-transistor, one-capacitor-type memory cells in which correct data can be read out even if a fluctuation in the power supply voltage is generated.

According to the present invention, there is provided a dynamic RAM device; first and second power supplies, the potential of the first power supply being lower than that of the second power supply; a first clock generator for generating a first clock signal having a potential higher than that of the second power supply and a second clock signal having a potential lower than or equal to the potential of the second power supply; a second clock generator for generating a third clock signal having a potential higher than the potential of the second power supply alternately with the first and second clock signals; a plurality of word lines selectively driven by the first clock signal; a plurality of pairs of bit lines precharged by the second power supply in response to the third clock signal; a plurality of sense amplifiers, each sense amplifier being arranged between one pair of the pairs of bit lines, for sensing the difference in potential between the pairs of bit lines; a plurality of one-transistor, one-capacitor-type memory cells in rows and columns, each memory cell being connected to one of the word lines and to one of the bit lines; a plurality of dummy cells, each dummy cell comprising a capacitor and a connection node, the capacitor having an electrode connected to one of the bit lines and another electrode connected to one of the connection nodes; at least one charging means, each means being connected to each of the connection nodes of the dummy cells respectively and driven by the third clock generator, for charging the capacitor of each of the dummy cells; and at least one discharging means, each means being connected to each of the connection nodes of the dummy cells respectively and driven by the second clock signal, for discharging the capacitor of each of the dummy cells.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from the description as set forth below contrasting the present invention with the prior art and referring to the accompanying drawings, wherein:

FIG. 1 is a block circuit diagram of a prior art dynamic RAM device;

FIG. 2 is a partial circuit diagram of the circuit of FIG. 1;

FIG. 3 is a circuit diagram of another prior art dynamic RAM device;

FIGS. 4A and 4B are timing diagrams of the signals appearing in the circuit of FIG. 3;

FIG. 5 is a circuit diagram of a first embodiment of the dynamic RAM device according to the present invention;

FIGS. 6A and 6B are timing diagrams of the signals appearing in the circuit of FIG. 5;

FIG. 7 is a circuit diagram of a second embodiment of the dynamic RAM device according to the present invention;

FIGS. 8A and 8B are also timing diagrams of the signals appearing in the circuit of FIG. 5; and

FIG. 9 is a circuit diagram of a third embodiment of the dynamic RAM device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, the prior art dynamic RAM devices will be explained with reference to FIGS. 1, 2, 3, 4A, and 4B. In FIG. 1, for example, a 16 kbit (precisely, 16,384 bit) RAM device is illustrated. In the figure, one-transistor, one-capacitor-type memory cells C₀₀, C₀₁, . . . , C₀,127, C₆₃,0, C₆₃,1, . . . , C₆₃,127, C₆₄,0, C₆₄,1, . . . , C₆₄,127, C₁₂₇,0, C₁₂₇,1, . . . , and C₁₂₇,127 in rows and columns are arranged at intersections between word lines WL₀, . . . , WL₆₃, WL₆₄, . . . , and WL₁₂₇ and bit lines BL₀, BL₀, BL₁, BL₁, . . . , BL₁₂₇, and BL₁₂₇, and sense amplifiers S₀, S₁, . . . , and S₁₂₇ in a row are arranged between bit line pairs BL₀, BL₀, BL₁, BL₁ , . . . , BL₁₂₇, and BL₁₂₇. Further, dummy cells DC₁₀, DC₁₁, . . . , and DC₁,127 in a row are connected to the terminals of bit lines BL₀, BL₁, . . . , and BL₁₂₇ and to dummy word line DWL₁ while dummy cells DC₂₀, DC₂₁, . . . , and DC₂,127 in a row are connected to the terminals of bit lines BL₀, BL₁, . . . , and BL₁₂₇ and to dummy word line DWL₂.

In FIG. 1, φ_(WL) is an operation clock signal for driving word lines WL₀, . . . , WL₆₃, WL₆₄, . . . , and WL₁₂₇ and dummy word lines DWL₁ and DWL₂. φ_(R) is a reset clock signal for resetting capacitor Q_(R) (not shown in FIG. 1 but shown in FIG. 2) of each dummy cell and for precharging bit lines BL₀, BL₀, BL₁, BL₁, . . . , BL₁₂₇ and BL₁₂₇.

The selection of word lines WL₀, WL₁, . . . , and WL₁₂₇ is carried out by word decoders DEC, and, simultaneously, the selection of dummy word lines DWL₁ and DWL₂ is also carried out by row decoders DEC. For example, when one of the word lines WL₀ through WL₆₃ is selected, dummy word line DWL₂ is selected while when one of word lines WL₆₄ through WL₁₂₇ is selected, dummy word line DWL₁ is selected. Such selection is carried out by transfer gates TG₋₁, TG₀, . . . , TG₆₃, TG₆₄, . . . , TG₁₂₇, and TH₁₂₈ which are switched on by word decoders DEC so as to transfer the clock signal φ_(WL). In more detail, word decoders DEC decode row address signals A₀, A₀, A₁, A₁, . . . , A₅ and A₅ so that one of the transfer gates TG₀ through TG₁₂₇, that is, one of the word lines WL₀ through WL₁₂₇, is selected, and, in addition, row decoders DEC decode row address signal A₆ or A₆ so that one of the transfer gates TG₋₁ and TG₁₂₈, that is, one of the dummy word lines DWL₁ and DWL₂, is selected.

In FIG. 2, which is a partial circuit diagram of the circuit of FIG. 1, word line WL₀ and dummy word line DWL₂ of FIG. 1 are illustrated in detail while the other word lines and dummy word line DWL₁ are omitted. That is, if word line WL₀ is selected, dummy word line DWL₂ on the opposite side regarding the sense amplifiers is always selected.

Each of memory cells C₀₀, C₀₁, . . . , and C₀,127 comprises capacitor C_(m) and transistor Q_(m) while each of the dummy cells DC₂₀, DC₂₁, . . . , and DC₂,127 comprises capacitor C_(d), transistor Q_(d), and transistor Q_(R). In this case, the capacitance of each capacitor C_(d) of the dummy memory cells is set to be about half the capacitance of each capacitor C_(m) of the memory cells. During the standby mode, reset clock generator CK₂ generates reset clock signal φ_(R) having a potential higher than V_(CC) +V_(th), where V_(th) is the common threshold voltage value of the enhancement transistors. As a result, capacitors C_(d) of the dummy cells D₂₀, D₂₁, . . . , and DC₂,127 are discharged, and, simultaneously, bit lines BL₀, BL₀, BL₁, BL₁, . . . , BL₁₂₇, and BL₁₂₇ are precharged to a potential V_(CC). Next, during the selecting mode, operation clock generator CK₁ supplies a clock signal φ_(WL) through on-state transfer gates TG₀ and TG₁₂₈ to a word line WL₀ and a dummy word line DWL₂, which means that the word line WL₀ and the dummy word line DWL₂ are selected. As a result, for example, when the potential of capacitor C_(m) of the memory cell C₀₀ is high (which corresponds to data "1", for example), the potential of the bit line BL₀ does not decrease while when the potential of the capacitor C_(m) of the memory cell C₀₀ is low (which corresponds to data "0" ), the potential bit line BL₀ decreases. On the other hand, in the dummy cell DC₂₀, since capacitor C_(d) is charged, bit line BL₀ decreases. In any case, since the capacitance of the capacitor C_(m) is different from that of the capacitor C_(d), there is generated a difference in potential between bit lines BL₀ and BL₀. Such difference in potential is sensed, that is, enlarged, by the sense amplifier S₀, and the difference is then read out.

In FIG. 2, however, the load of operation clock generator CK₁ is dependent on not only the capacity of the word line WL₀, the capacity of the gates of the transistors Q_(m) of the memory cells C₀₀, C₀₁, . . . , and C₀,127, and the like, but also is dependent upon the capacity of the dummy word line DWL₂, the capacity of the gates of the dummy cells DC₂₀, DC₂₁, . . . , DC₂,127, and the like. Therefore, the load of the operation clock generator CK₁ is large, so that the operation speed of the device is reduced.

FIG. 3 is a circuit diagram illustrating another prior art dynamic RAM device which is disclosed in FIG. 8 of the IEEE Journal of Solid-State Circuits, vol. SC-15, No. 2, pp. 184-189, April 1980. In FIG. 3, word lines WL₀ and dummy word line DWL₁ are illustrated in detail while the other word lines and dummy word line DWL₂ are omitted. That is, if word line WL₀ is selected, dummy word line DWL₁ on the same side regarding sense amplifiers S₀ ', S₁ ', S₂ ', . . . , and S₆₃ ' is always selected.

Each of dummy cells DC₁₀ ', DC₁₁ ', . . . , and DC₁,127 ' comprises only one capacitor C_(d), thereby remarkably reducing the area occupied by the dummy cells in the chip as compared with the dummy memory cells of FIG. 2. Q_(A) and Q_(B) are charging and discharging transistors, respectively, for dummy word line DWL₁, that is, for capacitors C_(d). Charging transistor Q_(A) is clocked by the clock signal φ_(WL) generated by the operation clock generator CK₁, while discharging transistor Q_(B) is clocked by the clock signal φ_(R) generated by the reset clock generator CK₂. Therefore, the load of the operation clock generator CK₁ is dependent on the capacity of the charging transistor Q_(A) in addition to the capacity of the word line WL₀, the capacity of the gates of transistors Q_(m) of the memory cells C₀₀, C₀₁, . . . , and C₀,127, and the like, thereby reducing the load of the operation clock generator CK₁.

The operation of the circuit of FIG. 3 will now be explained with reference to FIG. 4A regarding only bit lines BL₀ and BL₁ since the sense amplifier S₀ ' responds to the pair of bit lines BL₀ and BL₁. Assuming memory cell C₀₀ stores data "1", that is, that the capacitor C_(m) of memory cell C₀₀ is charged, during the standby mode, the reset clock signal is high (V_(CC) +V_(th) +α), discharging transistor Q_(B) is turned on so that the capacitors C_(d) of the dummy cells DC₁₀ ', DC₁₁ ', . . . , DC₁,126 ', and DC₁,127 ' are discharged, and, accordingly, the potential of the dummy word line DWL₁ remains low (V_(SS) =ground level). Simultaneously, bit lines BL₀, BL₀, BL₁, BL₁, . . . , BL₁₂₆, BL₁₂₆, BL₁₂₇, and BL₁₂₇ are precharged to level V_(CC). Next, during the selecting mode, the potential of clock signal φ_(R) is changed from the level V_(CC) +V_(th) +α to the level V_(SS), and, in addition, the potential of the clock signal φ_(WL) is changed from the level V_(SS) to the level V_(CC) +V_(th) +α. As a result, the potential of the word line WL₀ selected by the decorder DEC is changed in common phase with the potential of the clock signal φ_(WL). In addition, discharging transistor Q_(B) is turned off while charging transistor Q_(A) is turned on. As a result, the potential of the selected dummy word line DWL₁ is changed in common phase with the potential of the clock signal φ_(WL). Simultaneously, the bit lines assume a floating state. In this case, since bit line BL₀ is connected to dummy word line DWL₁ by the capacitive coupling of capacitors C_(d), the potential of the bit line BL₀ is pulled up in proportion to the capacitance ratio of the bit line BL₀ to the dummy word line DWL₁. That is, the potential of dummy word line DWL₁ causes the potential of bit line BL₀ to be slightly positive relative to the potential of bit line BL₁. Thus, a difference ΔV_(BL) in potential is generated between bit lines BL₀ and BL₁ , and, during the sensing mode, such difference is sensed by sense amplifier S₀ '. As a result, the lower-side potential of bit line BL₁ is decreased to V_(SS).

Similarly, assuming that the memory cell C₀₀ stores data "0", that is, that capacitor C_(m) of the memory cell C₀₀ is discharged, the potential of dummy word line DWL₁ also causes the potential of bit line BL₀ to be high. However, current flows from the bit line BL₀ into the capacitor C_(m) of the memory cell C₀₀, and, accordingly, the potential of the bit line BL₀ is pulled down in proportion to the capacitance ratio of the capacitor C_(m) of the memory cell C₀₀ to the bit line BL₀. Then, as illustrated in FIG. 4B, the potential of the bit line BL₀ becomes slightly negative relative to the potential of bit line BL₁. Thus, a difference ΔV_(BL) ' in potential is generated between bit lines BL₀ and BL₁, and, during the sensing mode, such difference ΔV_(BL) ' in potential is sensed by the sense amplifier S₀ '. As a result, the lower-side potential of bit line BL₀ is decreased to V_(SS).

In the dynamic RAM device of FIG. 3, however, in order to push up the potential of the dummy word line DWL₁ to the level V_(CC), the operation clock generator CK₁ must generate a potential higher than V_(CC) +V_(th), that is, a potential of V_(CC) +V_(th) +α, and, the accordingly, operation clock generator CK₁ must incorporate a charge-pumping circuit or a bootstrap circuit each of which is not provided with the capability of quickly driving a heavy load including both the dummy word line DWL₁ and the word line WL₀. Therefore, the operation speed of row selection, that is, the access speed of the device, becomes low.

FIG. 5 is a circuit diagram of a first embodiment of the dynamic RAM device according to the present invention. In FIG. 5 the elements which are the same as those of FIG. 3 are denoted by the same reference numerals as in FIG. 3. As the figure shows, if word line WL₀ is selected, dummy word line DWL₂ on the opposite side regarding the sense amplifiers S₀, S₁, . . . , and S₁₂₇ is selected. In addition, the charging transistor Q_(A) is connected to the reset clock generating circuit CK₂ while the discharging transistor Q_(B) is connected through transfer gate TG₁₂₈ to the operation clock signal generating circuit CK₁ which generates clock pulses φ_(WL) and φ_(WL) ' in reciprocal phase with the reset pulse φ_(R).

The operation of the circuit of FIG. 5 regarding only bit lines BL₀ and BL₀ will now be explained with reference to FIG. 6A. Assuming that memory cell C₀₀ stores data "1", that is, that capacitor C_(m) of memory cell C₀₀ is charged, during the standby mode, the reset clock signal φ_(R) is high (V_(CC) +V_(th) +α), charging transistor Q_(A) is turned on so that capacitors C_(d) of dummy cells DC₂₀ ', DC₂₁ ', . . . , DC₂,126 ', and DC₂,127 ' are charged, and, accordingly, the potential of dummy word line DWL₂ remains high (V_(CC)). Simultaneously, bit lines BL₀, BL₀, BL₁, BL₁, . . . , BL₁₂₆, BL₁₂₆, BL₁₂₇, and BL₁₂₇ are precharged to level V_(CC). Next, during the selecting mode, the potential of clock signal φ_(R) is changed from the level V.sub. CC +V_(th) +α to the level V_(SS), however, the potential of clock signal φ_(WL) is changed from the level V_(SS) to the level V_(CC) +V_(th) +α. As a result, the potential of a selected word line WL₀ is changed in response to the potential of the clock signal φ_(WL). When clock signal φ_(WL) is changed, clock generator CK₁ simultaneously generates the clock signal φ_(WL) ' which is changed from V_(SS) to V_(CC) in common phase with the clock signal φ_(WL). Thus, charging transistor Q_(A) is turned off while discharging transistor Q_(B) is turned on. As a result, the potential of dummy word line DWL₂ is changed in opposite phase to the potential of clock signal φ_(WL) '. Simultaneously, the bit lines assume a floating state. In this case, since bit line BL₀ is connected to dummy word line DWL₂ by the capacitive coupling of capacitors C_(d), the potential of bit line BL₀ is pulled down by an amount in proportion to the capacitance ratio of dummy cell capacitor C_(d) to bit line BL₀. That is, the potential of dummy word line DWL₂ pulls down the potential of bit line BL₀ so that it is slightly negative relative to the potential of bit line BL₀. Thus, a difference ΔV_(BL) in potential is generated between bit lines BL₀ and BL₀, and, during the sensing mode, such difference is sensed by sense amplifier S₀. As a result, the lower-side potential of bit line BL₀ is decreased to V_(SS).

Similarly, assuming that memory cell C₀₀ stores data "0", that is, the capacitor C_(m) of memory cell C₀₀ is discharged and the potential of dummy word line DWL₂ also pulls down the potential of bit line BL₀. However, current flows from bit line BL₀ into capacitor C_(m) of memory cell C₀₀ and, accordingly, the potential of bit line BL₀ is also pulled down by the capacity ratio of capacitor C_(m) of memory cell C₀₀ to bit line BL₀. Dummy cell capacitor C_(d) is designed to have about half of the capacitance of one memory cell capacitor C_(m). Then, as illustrated in FIG. 6B, the potential of bit line BL₀ becomes slightly negative relative to the potential of bit line BL₀. Thus, a difference in potential ΔV_(BL) ' is generated between bit lines BL₀ and BL₀, and, during the sensing mode, such difference in potential is sensed by sense amplifier S₀. As a result, the lower-side potential of bit line BL₀ is decreased to V_(SS).

In the dynamic RAM device of FIG. 5, operation clock generator CK₁ generates clock signals φ_(WL) having level V_(CC) +V_(th) +α and φ_(WL) ' having level V_(CC). However, it should be noted that the load driven by the clock signal φ_(WL) which requires a high level V_(CC) +V_(th) +α is reduced. As stated above, a clock signal having a level higher than V_(CC) is generated by a charge-pumping circuit, bootstrap circuit, or the like which usually has only an ability to drive a small load. Therefore, if the load which requires a clock signal having a level higher than V_(CC) is small, the operation speed of the operation clock generator CK₁ becomes high. As a result, the access speed of the device becomes high.

Note that generally in a memory device, the highest priority of design is to reduce the access time. Therefore, although reset clock generator CK₂ incorporates a charge-pumping circuit or a bootstrap circuit for generating a potential higher than V_(CC), this is not disadvantageous since the reset operation does not affect the access speed.

FIG. 7 is a circuit diagram of a second embodiment of the dynamic RAM according to the present invention. In FIG. 7, each of dummy cells DC₂₀ "', DC₂₁ "', . . . , and DC₂,127 "' comprises a discharging transistor Q_(B) ', for discharging capacitor C_(d), instead of the discharging transistor Q_(B) of FIG. 5. In this case, discharging transistors Q_(B) ' are smaller than discharging transistor Q_(B) of FIG. 5. However, the operation of the circuit of FIG. 7 is substantially the same as that of the circuit of FIG. 5. Note that, in this case, dummy word line DWL₂ ' is not directly connected to capacitors C_(d) of dummy cells DC₂₀ ", DC₂₁ ", . . . , and DC₂,127 ". In addition, the potential at node N₀, N₁, . . . , or N₁₂₇ of FIG. 7 corresponds to the potential of dummy word line DWL₂ of FIG. 5.

FIGS. 8A and 8B are also timing diagrams of the signals appearing in the circuit of FIG. 5 (or 7). In FIGS. 8A and 8B, it is assumed that the potential of the power supply V_(CC) fluctuates at the transition from the standby mode to the selecting mode. That is, since charging transistor Q_(A) is relatively large, the potential of dummy word line DWL₂ rapidly follows the fluctuation of the power supply potential V_(CC). However, since the bit lines have a large capacitance and, in addition, the precharging transistors are relatively small so as to limit current therethrough, the potential of the bit lines responds very slowly to fluctuation of the power supply voltage V_(CC).

In FIG. 8A, which corresponds to FIG. 6A, the power supply potential is decreased from V_(CC) to V_(CC) -ΔV_(CC). In this case, the potential of bit line BL₀ is not as decreased as in FIG. 6A. That is, in the case of reading data "1", the difference ΔV_(BL) in potential becomes small. Consequently, the sensing speed is reduced, and an erroneous read operation may result. However, in FIG. 8B, which corresponds to FIG. 6B, the power supply potential is increased from V_(CC) to V_(CC) +ΔV_(CC). In this case, the potential of bit line BL₀ is decreased greatly as compared with FIG. 6B. That is, in the case of reading data "0", the difference ΔV_(BL) ' in potential also becomes small. Consequently, the sensing speed is reduced, and an erroneous read operation may result.

In order to avoid fluctuation of the potential of the bit lines due to fluctuation of a power supply potential, according to the present invention, capacitor C_(d) of the dummy cell can also be charged by using the potential of the corresponding bit line.

FIG. 9 is a circuit diagram of a third embodiment of the dynamic RAM device according to the present invention. In FIG. 9, each of dummy cells DC₂₀ "', DC₂₁ "', . . . , and DC₂,127 "' comprises a charging transistor Q_(A) ' instead of charging transistor Q_(A) of the FIG. 7. That is, charging transistor Q_(A) ' of dummy cell DC₂₀ "' is connected between bit line BL₀ and node N_(O). Therefore, during the standby mode, even when power supply potential V_(CC) fluctuates rapidly, the potential at node N₀, N₁, . . . , or N₁₂₇ of capacitors C_(d) remains stable since the potential at node N₀, N₁, . . . , or N₁₂₇ follows the potential of bit line BL₀, BL₁, . . . , or E,ovs/BL/ ₁₂₇, which potential does not fluctuate as much. Therefore, the above-mentioned unfavorable difference in potential, which reduces the sensing speed and may result in an erroneous read operation is not generated.

As explained hereinbefore, the dynamic RAM device according to the present invention is advantageous, as compared with the prior art as illustrated in FIG. 3, in that the access speed is high since it is unnecessary that the operation clock generator CK₁ drive a heavy load requiring a potential higher than V_(CC) during the selecting operation. 

We claim:
 1. A dynamic random access memory device, comprising:first and second power supplies, the potential of said first power supply being lower than that of said second power supply; a first clock generator, operatively connected to said second power supply, for generating a first clock signal having a potential higher than the potential of the second power supply and a second clock signal having a potential lower than or equal to the potential of said second power supply; a second clock generator, operatively connected to said second power supply, for generating a third clock signal having a potential higher than the potential of said second power supply, said third clock signal generated alternately with said first and second clock signals; a plurality of word lines, operatively connected to said first clock generator, selectively driven by said first clock signal; a plurality of pairs of bit lines, intersecting said word lines, each said pair of bit lines operatively connected to said second clock generator and precharged by said second power supply in response to said third clock signal; a plurality of sense amplifiers, respectively, operatively connected between said pairs of bit lines, for sensing the difference in potential between each of said pairs of bit lines; a plurality of one-transistor, one-capacitor-type memory cells, respectively, operatively connected at said intersections of said word lines and said bit lines; a plurality of dummy cells, respectively, operatively connected to each of said bit lines, each of said dummy cells comprising:a capacitor having a first electrode connected to one of said bit lines and a second electrode; and a connection node located between said second electrode of said capacitor and said second clock generator; at least one charging means, each said at least one charging means operatively connected to said connection nodes of said dummy cells, respectively, and operatively connected to said second clock generator, for charging said capacitor of each of said dummy cells upon receipt of said third clock signal; andat least one discharging means, each discharging means operatively connected to said connection nodes of said dummy cells, respectively, and operatively connected to said first clock generator, for discharging said capacitor of each of said dummy cells upon receipt of said second clock signal.
 2. A device as set forth in claim 1, wherein each said discharging means comprises a transistor having a drain operatively connected to said connection nodes of said dummy cells, having a gate, operatively connected to said first clock generator, for receiving said second clock signal, and having a source operatively connected to said first power supply.
 3. A device as set forth in claim 1, wherein each said discharging means comprises a transistor, included in each of said dummy cells, having a drain operatively connected to said connection node of a respective one of said dummy cells having a gate operatively connected to said first clock generator, for receiving said second clock signal, and having a source operatively connected to said first power supply.
 4. A device as set forth in claim 1, wherein each said charging means comprises a transistor having a drain operatively connected to said second power supply, having a gate operatively connected to said second clock generator for receiving said third clock signal, and having a source operatively connected to said connection nodes of said dummy cells.
 5. A device as set forth in claim 1, wherein each said charging means comprises a transistor, included in each of said dummy cells, having a drain operatively connected to a respective bit line, having a gate operatively connected to said second clock generator for receiving said third clock signal, and having a source operatively connected to said connection node of a respective one of said dummy cells.
 6. A dynamic random access memory device, operatively connected to first and second power supplies, the first potential of the first power supply begin less than the second potential of the second power supply, comprising:a first clock generator, operatively connected to the second power supply, for generating a first clock signal having a third potential greater than the second potential of the second power supply, and a second clock signal having a fourth potential less than or equal to the second potential of the second power supply; a second clock generator, operatively connected to the second power supply, for generating a third clock signal having a fifth potential greater than the second potential of the second power supply, the third clock signal generated alternately with the first and second clock signals; word lines, operatively connected to said first clock generator, selectively driven by the firt clock signal; pairs of bit lines intersecting said word lines and operatively connected to said second clock generator, each of said pairs of bit lines having a potential and being precharged by the second power supply in response to the third clock signal; sense amplifiers, respectively, operatively connected between said pairs of bit lines, for sensing the difference in potential between said pairs of bit lines; one-transistor, one-capacitor-type memory cells, respectively, operatively connected at said intersections of said word lines and said bit lines; dummy cells, respectively, operatively connected to each of and said bit lines, each of said dummy cells comprising:a capacitor having a first electrode operatively connected to one of said bit lines and having a second electrode; and a connection node located between said second electrode of said capacitor and said second clock generator; charging means, operatively connected to each of said connection nodes and connected to said second clock generator, for receiving the third clock signal and for charging said capacitor of each of said dummy cells; and discharging means, operatively connected to each of said connection nodes of said dummy cells and connected to said second clock generator, for receiving the third clock signal and for discharging said capacitor of each of said dummy cells.
 7. A dynamic random access memory device as set forth in claim 6, wherein said discharging means comprises a transistor having a drain, respectively, operatively connected to said connection nodes, having a gate operatively connected to said first clock generator for receiving the second clock signal, and having a source operatively connected to the first power supply.
 8. A dynamic random access memory device as set forth in claim 6, wherein said discharging means comprises a transistor included in each of said dummy cells, said transistor having a drain, respectively, operatively connected to said connection node of said dummy cells, having a gate operatively connected to said first clock generator for receiving the second clock signal, and having a source operatively connected to the first power supply.
 9. A dynamic random access memory device as set forth in claim 6, wherein said charging means comprises a transistor having a drain operatively connected to the second power supply, having a gate operatively connected to said second clock generator for receiving the third clock signal, and having a source, respectively, operatively connected to said connection node of said dummy cells.
 10. A dynamic random access memory device as set forth in claim 6, wherein said charging means comprises a transistor included in each of said dummy cells, having a drain operatively connected to one of said bit lines, having a gate operatively connected to said second clock generator for receiving the third clock signal, and having a source, respectively, operatively connected to said connection node of said dummy cells.
 11. A device as set forth in claim 6, wherein said discharging means comprises a transistor included in each of said dummy cells, having a drain, respectively, operatively connected to said connection node of said dummy cells, having a gate operatively connected to said first clock generator for receiving the second clock signal, and having a source operatively connected to the second power supply.
 12. A device as set forth in claim 7, wherein said charging means comprises a transistor having a drain operatively connected to the second power supply, having a gate operatively connected to said second clock generator for receiving the third clock signal, and having a source, respectively, operatively connected to said connection node of said dummy cells. 